1. Field of the Invention
The present invention relates to a wireless local area network (WLAN) system, and more particularly, to a method for determining a channel and for performing communication in the WLAN system.
2. Discussion of the Related Art
With the advancement of information communication technologies, various wireless communication technologies have recently been developed. Among the wireless communication technologies, a wireless local area network (WLAN) is a technology whereby Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
Ever since the institute of electrical and electronics engineers (IEEE) 802, i.e., a standardization organization for WLAN technologies, was established in February 1980, many standardization works have been conducted.
In the initial WLAN technology, a frequency of 2.4 GHz was used according to the IEEE 802.11 to support a data rate of 1 to 2 Mbps by using frequency hopping, spread spectrum, infrared communication, etc. Recently, the WLAN technology can support a data rate of up to 54 Mbps by using orthogonal frequency division multiplex (OFDM). In addition, the IEEE 802.11 is developing or commercializing standards of various technologies such as quality of service (QoS) improvement, access point protocol compatibility, security enhancement, radio resource measurement, wireless access in vehicular environments, fast roaming, mesh networks, inter-working with external networks, wireless network management, etc.
The IEEE 802.11n is a technical standard relatively recently introduced to overcome a limited data rate which has been considered as a drawback in the WLAN. The IEEE 802.11n is devised to increase network speed and reliability and to extend an operational distance of a wireless network. More specifically, the IEEE 802.11n supports a high throughput (HT), i.e., a data processing rate of up to above 540 Mbps, and is based on a multiple input and multiple output (MIMO) technique which uses multiple antennas in both a transmitter and a receiver to minimize a transmission error and to optimize a data rate.
An IEEE 802.11n HT WLAN system employs an HT green field physical layer convergence procedure (PLCP) protocol data unit (PPDU) format which is a PPDU format designed effectively for an HT station (STA) and which can be used in a system consisting of only HT STAs supporting IEEE 802.11n in addition to a PPDU format supporting a legacy STA. In addition, an HT-mixed PPDU format is supported as a PPDU format designed to support an HT system in a system in which the legacy STA and the HT STA coexist.
With the widespread use of the WLAN and the diversification of applications using the WLAN, there is a recent demand for a new WLAN system to support a higher throughput than a data processing rate supported by the IEEE 802.11n. A next-generation WLAN system supporting a very high throughput (VHT) is a next version of the IEEE 802.11n WLAN system, and is one of IEEE 802.11 WLAN systems which have recently been proposed to support a data processing rate of above 1 Gbps in a MAC service access point (SAP).
The next generation WLAN system allows simultaneous channel access of a plurality of VHT STAs for the effective use of a radio channel. For this, multi-user multiple input multiple output (MU-MIMO)-based transmission using multiple antennas is supported. The VHT AP can perform spatial division multiple access (SDMA) transmission for transmitting spatial-multiplexed data to the plurality of VHT STAs. When data is simultaneously transmitted by distributing a plurality of spatial streams to the plurality of STAs by using a plurality of antennas, an overall throughput of the WLAN system can be increased.
The IEEE 802.11n standard represented as the existing HT WLAN system supports a transmission channel having a bandwidth of 20 MHz and 40 MHz. In addition thereto, the next generation WLAN system intends to support a transmission channel having a bandwidth of 20 MHz, 40 MHz, 80 MHz, contiguous 160 MHz, and non-contiguous 160 MHz (80+80) or a bandwidth of a broader band. To provide a throughput of 1 Gbps or higher, a feasibility test is currently being conducted for the VHT system using 4×4 MIMO and a channel bandwidth of 80 MHz or higher.
However, in general, a case where an 80 MHz bandwidth can be fully used by different communication systems or devices that use the same frequency band may be very limited. In addition, since a hotspot for providing a WLAN service is increased as the WLAN is widely used and utilized, an overlapping basic service set (OBSS) environment is increased in which a basic service area (BSA) which is a service area of that hotspot overlaps partially or fully. In the OBSS environment, in addition to the existing WLAN system, there is a need to consider a method for determining a channel to be used and for performing communication according to a channel condition of each of all available bandwidths and an apparatus for supporting the method.